1. Field of the Invention
The present invention pertains to the techniques for imparting driving forces for moving loads. More particularly, the present invention relates to apparatus for coupling propulsion mechanisms with closure devices such as gates for transmitting driving forces thereto for opening and/or closing such devices. Apparatus according to the present invention finds specific application to slide gates used to selectively open and close passageways against the flow of material therethrough. Such slide gates, for example, may be mounted at the base of storage bins to control the removal of material from the storage bins through passageways of chutes.
2. Description of Prior Art
Storage bins, or hoppers, are often equipped with passageways emerging from the bottom of the bins whereby material stored in the bins may be selectively removed. A door, or gate, closes the passageway when material is to be stored in the bin, and then may be opened to allow material to flow down out of the bin. Such doors operate essentially as valves to control the quantity of material removed from the bins.
The bin doors, or gates, may be manually operated, or, particularly where such doors comprise large loads to move, may be operated by motors. In the latter case, such motors may, in turn, be automatically controlled to open and/or close the bin doors on command or in response to the occurence of predetermined conditions. For example, where sensors are employed to detect the level of materials in the bin control devices may be appropriately triggered to open the bin doors when the material level reaches a predetermined position within the bin. Such level detectors are discussed in detail in U.S. Pat. Nos. ,3,807,231 and 3,935,970, and U.S. Pat. applications Ser. Nos. 844,040 and 877,028, filed Oct. 20, 1977 and Feb. 10, 1978, respectively.
With the passage door or gate located towards the bottom of the bin, the gate in the closed configuration is required to support a significant portion of the weight of the material stored in the bin. Consequently, the gate must be constructed and mounted to provide a sufficiently strong support. Furthermore, the gate will often be structured as a slide gate rather than a swinging door mounted on hinges. Where the passageway is to be closed while material still remains in the bin, a sliding gate may generally be more easily moved into a close configuration rather than a swinging door which must be drawn up against the flow of material through the passage. Also, a sliding gate may be held in a partially open position with support around a greater portion of its periphery than may a swinging door.
The weight of material stored in the bin acting on a slide gate closing a passage at the bottom of the bin generates retarding forces which resist sideways movement of the slide gate to open the passage. Such retarding forces depend not only on the weight and quantity of the material in the bin, but also on the cohesiveness of the material and the degree to which it adheres to the surface of the gate. Such forces may be relatively large and, combined with the inertia of the gate itself, may provide a substantial force barrier which must be overcome by whatever means is used to impart driving forces to move the gate. Once the static friction retarding forces due to the material resting on the gate are overcome and the gate is in motion, the force applied to keep the gate in motion may be decreased. Consequently, the means employed for propelling the gate in such a situation is called upon to generate the greatest forces when the propulsion means itself is just starting in motion from a standing condition. Electric motors, which are usually used to operate such bin gates, are generally known to have the least force generating capacity under such start up conditions. Consequently, such a motor, or the linkage between the motor and the slide gate, may slip until sufficient momentum has been generated within the motor and the linkage to apply a sufficiently large force to overcome the motion retarding forces. In such applications, the driving motor may also be subject to over heating and excessive wear during such start up operations. A by-product of such an inefficient operation is waste of energy.